1. Field of the Invention
The invention relates generally to a method for creating a microarray of biomaterial by direct writing of a wide range of different biomaterials onto a substrate.
2. Description of the Prior Art
The term “direct write” refers generally to any technique for creating a pattern directly on a substrate, either by adding or removing material from the substrate, without the use of a mask or preexisting form. Direct write technologies have been developed in response to a need in the electronics industry for a means to rapidly prototype passive circuit elements on various substrates, especially in the mesoscopic regime, that is, electronic devices that straddle the size range between conventional microelectronics (sub-micron-range) and traditional surface mount components (10+ mm-range). (Direct writing may also be accomplished in the sub-micron range using electron beams or focused ion beams, but these techniques, because of their small scale, are not appropriate for large-scale rapid prototyping.) Direct writing allows for circuits to be prototyped without iterations in photolithographic mask design and allows the rapid evaluation of the performance of circuits too difficult to accurately model. Further, direct writing allows for the size of printed circuit boards and other structures to be reduced by allowing passive circuit elements to be conformably incorporated into the structure. Direct writing methods for transferring electronic materials can also be useful for transferring biomaterials to make simple or complex biomaterial structures, with or without associated electronic circuitry. Direct writing can be controlled with CAD/CAM programs, thereby allowing electronic circuits to be fabricated by machinery operated by unskilled personnel or allowing designers to move quickly from a design to a working prototype. Mesoscopic direct write technologies have the potential to enable new capabilities to produce next generation applications in the mesoscopic regime.
Currently known direct write technologies for adding materials to a substrate include ink jet printing, Micropen® laser chemical vapor deposition (LCVD), laser particle guidance (Optomec, Inc.), and laser engineered nano-shaping (LENS). Currently known direct write technologies for removing material from a substrate include laser machining, laser trimming and laser drilling.
The direct writing techniques of ink jet printing, screening, and Micropen® are wet techniques, that is, the material to be deposited is combined with a solvent or binder and is squirted onto a substrate. The solvent or binder must later be removed by a drying or curing process, which limits the flexibility and capability of these approaches. In addition, wet techniques are inherently limited by viscoelastic properties of the fluid in which the particles are suspended or dissolved.
In the direct writing technique known as “laser induced forward transfer” (LIFT), a pulsed laser beam is directed through a laser-transparent target substrate to strike a film of material coated on the opposite side of the target substrate. The laser vaporizes the film material as it absorbs the laser radiation and, due to the transfer of momentum, the material is removed from the target substrate and is redeposited on a receiving substrate that is placed in proximity to the target substrate. Laser induced forward transfer is typically used to transfer opaque thin films, typically metals, from a pre-coated laser transparent support, typically glass, SiO2, Al2O3, SrTiO3, etc., to the receiving substrate. Various methods of laser-induced forward transfer are described in, for example, the following U.S. patents and publications incorporated herein by reference: U.S. Pat. No. 4,752,455 to Mayer, U.S. Pat. No. 4,895,735 to Cook, U.S. Pat. No. 5,725,706 to Thoma et al., U.S. Pat. No. 5,292,559 to Joyce, Jr. et al., U.S. Pat. No. 5,492,861 to Opower, U.S. Pat. No. 5,725,914 to Opower, U.S. Pat. No. 5,736,464 to Opower, U.S. Pat. No. 4,970,196 to Kim et al., U.S. Pat. No. 5,173,441 to Yu et al., and Bohandy et al., “Metal Deposition from a Supported Metal Film Using an Excimer Laser, J. Appl. Phys. 60 (4) Aug. 15, 1986, pp 1538-1539. Because the film material is vaporized by the action of the laser, laser induced forward transfer is inherently a homogeneous, pyrrolytic technique and typically cannot be used to deposit complex crystalline, multi-component materials or materials that have a crystallization temperature well above room temperature because the resulting deposited material will be a weakly adherent amorphous coating. Moreover, because the material to be transferred is vaporized, it becomes more reactive and can more easily become degraded, oxidized, or contaminated. The method is not well suited for the transfer of organic materials, since many organic materials are fragile, thermally labile, and can be irreversibly damaged during deposition. Moreover, functional groups on an organic polymer can be irreversibly damaged by direct exposure to laser energy. Neither is the method well suited for the transfer of biomaterials. The cells or biomolecules can be damaged during deposition. Other disadvantages of the laser induced forward transfer technique include poor uniformity, morphology, adhesion, and resolution. Further, because of the high temperatures involved in the process, there is a danger of ablation or sputtering of the support, which can cause the incorporation of impurities in the material that is deposited on the receiving substrate. Another disadvantage of laser induced forward transfer is that it typically requires that the coating of the material to be transferred be a thin coating, generally less that 1 μm thick. Because of this requirement, it is very time-consuming to transfer more than very small amounts of material.
In a simple variation of the laser induced forward deposition technique, the target substrate is coated with several layers of materials. The outermost layer, that is, the layer closest to the receiving substrate, consists of the material to be deposited and the innermost layer consists of a material that absorbs laser energy and becomes vaporized, causing the outermost layer to be propelled against the receiving substrate. Variations of this technique are described in, for example, the following U.S. patents and publications incorporated herein by reference: U.S. Pat. No. 5,171,650 to Ellis et al., U.S. Pat. No. 5,256,506 to Ellis et al., U.S. Pat. No. 4,987,006 to Williams et al., U.S. Pat. No. 5,156,938 to Foley et al. and Tolbert et al., “Laser Ablation Transfer Imaging Using Picosecond Optical pulses: Ultra-High Speed, Lower Threshold and High Resolution” Journal of imaging Science and Technology, Vol. 37, No. 5, September/October 1993 pp. 485-489. A disadvantage of this method is that, because of the multiple layers, it is difficult or impossible to achieve the high degree of homogeneity of deposited material on the receiving substrate required, for example, for the construction of electronic devices, sensing devices or passivation coatings.
U.S. Pat. No. 6,177,151 to Chrisey et al. discloses the MAPLE-DW (Matrix Assisted Pulsed Laser Evaporation Direct Write) method and apparatus. The method comprises the use of laser energy to cause a composite material to volatilize, desorb from a laser-transparent support, and be deposited on a receiving substrate. The composite material comprises a matrix material and a transfer material. The transfer material is the material desired to be transferred to the receiving substrate. The matrix material is more volatile than the transfer material and binds the transfer material into the composite material. The laser energy causes the matrix material to volatilize and propel the transfer material onto the receiving substrate. The properties of the transfer material are preserved after deposition. This method will be further described in the Detailed Description of the Preferred Embodiments below.
U.S. Pat. No. 6,177,151 is primarily directed to the transfer of electronic materials to form circuitry on the receiving substrate. It also discloses the transfer of chemoselective materials and bioselective materials. Examples of biochemical materials disclosed include proteins, oligopeptides, polypeptides, whole cells, biological tissue, enzymes, cofactors, nucleic acids, DNA, RNA, antibodies (intact primary, polyclonal, and monoclonal), antigens, oligosaccharides, polysaccharides, oligonucleotides, lectins, biotin, streptavidin, and lipids. The prior art does not disclose MAPLE-DW transfer of a microarray of biomaterials.
The biggest hurdle in creating a microarray of biomaterial is to maximize the density of spots and minimize consumption of biomaterial. Efficient use of materials is mandatory in order to fabricate protein identification arrays (because of the scarcity of desired protein solutions), and is preferred (both for cost and consumption of materials) for the fabrication of gene recognition arrays. Current state-of-the-art arraying techniques have a spot resolution of no less than 100 microns.
There is need for a method for transferring a microarray of biomaterial in such a way that desired properties of the biomaterials are preserved. A spot size of 10 microns is needed, allowing for a hundred-fold increase in spot density.